A speck of dust is 5.0×10 to the power of -7m wide. Which of the following is the best way to rewrite this quantity,using more appropriate units?
A.5.0×10 to the power of -5cm
B.5.0×10 to the power of -7m
C.5.0×10 to the power of -4mm
D.5.0×10 to the power of -10km